subroutine set_system_unit
  use global_param,only:unit_conv_order
  use global_param,only:sys_volume
  use box_param,only:bound
  use box_param,only:bwidth
  implicit none

  if (bwidth(1).lt.0.or.&
      bwidth(2).lt.0.or.&
      bwidth(3).lt.0) call abnormal_stop("set_system_unit",&
      "The size of simulation box is not specified.")

  unit_conv_order=0
  unit_conv_order=real(bound(1)+bound(2)+bound(3))

  sys_volume=1.0
  if (bound(1).eq.1) sys_volume=sys_volume*bwidth(1)
  if (bound(2).eq.1) sys_volume=sys_volume*bwidth(2)
  if (bound(3).eq.1) sys_volume=sys_volume*bwidth(3)

  return

end subroutine set_system_unit
